Various types of security systems to protect retail goods on display in a store are known throughout the trade. The basic components of the system include a sensor which is attached to each item of merchandise intended to be protected, a switch within the sensor which generates an alarm signal, splitter boxes or similar modular connecting units for receiving signals from the sensors, and an alarm box which is connected to the splitter boxes through various conducting cables and which houses an alarm.
Merchandise security systems can be broadly classified into two groups, closed loop and open loop systems. In a closed loop security system, current constantly flows from the alarm box to the sensor. The sensor switch is in a normally open state, i.e., a non-conducting state. Depressing the actuator of the switch would place the switch in a closed state, i.e., a conducting state. The sensor is attached to the article in such a manner that the actuator of the switch is depressed, placing the switch in its closed state, i.e. the contacts of the switch make or are electrically connected. After a sensor is attached to each item of merchandise, the alarm circuit is armed or set, usually with a key switch. When armed, the alarm box circuitry sends out a continuous current through the splitter boxes and sensor switches; the current then returns to the alarm box circuitry. A complete electrical circuit is formed when the switch is closed as a result of its attachment to an item of merchandise. As long as no cables are cut and the actuator remains depressed, a complete electrical circuit is made and the security system remains in its armed state.
During an unauthorized removal of the sensor, the actuator is distended, which opens the switch contacts and which breaks the closed loop circuit. Similarly, if a cable is cut the continuous current to the sensor is interrupted. The alarm box circuitry detects that the current has been interrupted and an alarm will sound. The alarm notifies store personnel that there has been a security breach.
A typical closed loop alarm system is disclosed in U.S. Pat. No. 4,746,909 (the '909 patent), issued May 24, 1988. The '909 patent discloses an electronic security system including a single control box, series connected modular sensor units, and conductive loop sensors attached to the modular monitoring units. A closed loop circuit is formed through the conductive loop sensors. The unauthorized removal of an item of merchandise will break or disconnect the conductive loop. This closed loop circuit will be broken; this disruption will be detected by the monitoring circuit which activates the alarm. A time-out circuit within the control box is used to determine the period of time in which the alarm is activated.
U.S. Pat. No. 3,253,270 discloses a battery-powered alarm in which separate long leads are connected to each of the goods to be protected. A first battery is used to power a detection circuit and a second battery is used to power an alarm circuit. A resistor is included with each sensor. The resistance of each sensor resistor must be substantially identical to the resistance of an internal circuit resistor. During a security breach, the current in the line will change, thus affecting the calibration of a meter in the detection circuit. When the needle of the meter is deflected far enough, an alarm is sounded.
The '270 patent also discloses a box to house the alarm circuitry. The box includes a lid which can be locked to the box. The lid is locked after the meter is adjusted to prevent tampering with the alarm system.
Another example of a closed loop system is U.S. Pat. No. 5,172,098, issued Dec. 18, 1992. The '098 patent discloses sensor switches on each sensor. During a security breach, the switch opens, breaking the closed loop. Detection circuitry determines that a security breach has occurred and turns on an audio and visual alarm.
The assignee of the '098 patent has developed several other closed loop security systems which operate in a manner similar to the '098 patent. For example, their Kord Kontrol.RTM. strip alarm system is another closed loop system. The Kord Kontrol.RTM. strip alarm is powered by two nine volt batteries with an AC adapter option. A switch within each sensor activates the alarm horn.
The assignee of the present application also has developed closed loop security systems. For example, the Electronic Merchant Guard (EMG-32) can be used with mechanical cables or electronic cables. The mechanical cables physically secure merchandise to a stationary box; the electronic cables carry a small DC voltage to electronic sensors which electrically secure merchandise. When merchandise is electrically secured, an alarm is sounded upon the detection of a security breach. The Electronic Merchant Guard houses the electronic circuitry in the same stationary box to which the mechanical cables are secured. A cover on the stationary box prevents tampering of the circuitry and locks the mechanical cables to the stationary box.
The assignee of the present application also manufactures SECURTRON (ES-24) which is a closed loop security system. The SECURTRON is easily adaptable to any fixture or wall system. Sensor clips or electronic cables are attached to the items or goods to be protected. The alarm circuitry is electronically connected to the sensor clips forming a closed loop circuit. When the cable is cut or is improperly removed, or when the security clip is removed without authorization, an alarm is activated.
A drawback of all closed loop security systems is that current must constantly flow. Accordingly, power must be supplied to the conductive loop or to the sensor switch at all times. Usually, the most feasible way to do this is to provide power via an AC/DC adapter. This presents a problem during power outages. Also, many stores turn off all power to the retail floor space at night or when the store is closed.
Battery backups have been designed to supply the necessary current; however, the current draw on the batteries is often too great to supply current for extended periods of time. This leaves the merchandise unprotected from unscrupulous security guards and support personnel (janitors, stock boys, etc.). In addition, batteries would need to be checked and replaced on a regular basis, increasing the maintenance of the security system. Recently, the situation has become more acute with the use of light emitting diodes (LEDs) on the splitter boxes and on the sensors. The LEDs add to the current drain making a battery back-up system an even less viable option.
Another drawback of many closed loop security systems is that they require jumpers or shunt plugs on the splitter box connections which are not connected to merchandise. The shunt plugs form an electrical connection to prevent the alarm from sounding when the system is armed. Shunt plugs increase the cost of the system and are also a source of misconnections if improperly installed. Further, shunt plugs must constantly be installed and removed as the items of merchandise are sold or as stock is replaced. Accordingly, the shunt plugs increase the amount of time store personnel must spend attending to the security system. In addition, if the required shunt plugs are lost or not installed properly the security system is inoperable since the alarm will sound continuously.
An open loop security system operates in a similar fashion to a closed loop system. However, the sensor switch would be normally closed, i.e. when the actuator is distended. When the sensor is properly attached to the merchandise, the actuator is depressed, opening the switch; this prevents current from flowing. If there is a tampering of the sensor switch, the actuator distends, the switch contacts close and current flows through the sensor switch. A continuous circuit is made when the sensor switch closes, activating the alarm.
In an open loop security system, the alarm does not sound unless a circuit is completed. Normally, the only way to complete the circuit is to remove the sensor from the article. Therefore, an open loop security system may be circumvented by cutting the sensor cable or removing the sensor cable plug from its jack. In this manner, the article may be stolen without the alarm sounding. Since open loop systems are easier to circumvent, they are not as popular as closed loop systems.
An open loop security system is disclosed in U.S. Pat. No. 4,620,182. This device includes a special cable which is designed to short out its internal wires if the cable is cut. When this cable is cut or damaged, a complete circuit is made thereby activating the alarm.
In many of the closed loop and open loop systems merchandise can be added while the security system is armed; either no alarm or only a short alarm will be activated. Continual short bursts from an alarm horn may annoy customers. In addition, many of these systems may be susceptible to circumvention since a foreign object may be connected to the security system to override the alarm.
The use of alarm modules or splitter boxes in security systems increases the maintenance of the security system. Extra connections are required to incorporate these splitter boxes; these extra connections are a weak link that can be attacked by a thief. In addition, many security systems require jumpers on all unused connections. Further, splitter boxes are unsightly to look at, and are a source of misconnections and false alarms.